A typical work machine may include a source of power fitted with a power train assembly to transfer the power from the power source to the power train assembly to do work. One common type of power train system includes a transmission, differential assembly and a pair of final drive assemblies configured to power a pair of ground engaging wheels which propel the work machine. Such power train systems may also be employed with stationary work systems, such as generators and compressors, used to create power or do work. Power train systems and particularly those used in agricultural machines such as tractors or other implement bearing machines typically include a common source of hydraulic fluid used to animate hydraulic implements, lubricate and cool moving power train components and activate steering systems. It is customary to employ a common sump or three interconnected non-pressurized fluid compartments, within the transmission, differential, and final drives assemblies, to lubricate moving componentry therein.
However, known systems employing the common sump may include an inadequate supply of fluid circulating across wet brake assemblies, resulting in elevated brake assembly temperatures. Previous common sump systems also may allow oil aeration which may lead to pump cavitation when the differential gears are allowed to rapidly rotate in a bath of fluid resulting in air being infused or entrained in the fluid. Cavitation may be decreased by limiting the amount of fluid in proximity to the differential. However, if an inadequate amount of lubrication fluid is provided to the differential premature bearing and gear wear may result.
One solution to improper fluid distribution in common sump applications is to increase the size of the fluid pump or add an additional pump to ensure a suitable amount of fluid is being distributed throughout the power train system. Typically, a conventional scavenge system will pull oil from one tank, the transmission sump for example, and dump it to another tank or oil housing such as the differential housing, for example. The addition of a scavenge system, such as the one described, lowers the fluid level in the transmission, to reduce power train parasitics (resistance due to gearing submersion in fluid) which increases fuel efficiency. Scavenge systems also decrease the required volume of fluid required to fill the system which results in a significant savings in cost. Moreover, scavenge systems may improve slope capability of the machine which, without the scavenge system, an abundance of fluid may accumulate in the differential when the machine is operating on a slope or hill.
U.S. Pat. No. 3,800,913 to Schmitt, issued Apr. 2, 1974, assigned to Caterpillar Inc., discloses a scavenge system for use with a power train assembly. An oil recirculation system employs a scavenge pump operative to scavenge the transmission sump and to recirculate oil from an overflow tank to a main supply tank. Although fluid circulation is enhanced, the significant additional costs associated with requiring an additional pump and adapting existing machines with the scavenging system may be undesirable.
A power train system which may overcome one or more of these limitations would be desirable. Furthermore, a power train system which does not significantly add cost relative to known power train assemblies, and one which may be readily adaptable to existing systems is highly desirable.